1. Technical Field
Exemplary aspects of the present invention relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device for fixing an image on a recording medium and an image forming apparatus incorporating the fixing device.
2. Description of the Background
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having two or more of copying, printing, scanning, facsimile, plotter, and other functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a development device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the photoconductor onto a recording medium or is indirectly transferred from the photoconductor onto a recording medium via an intermediate transfer belt; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
Such fixing device may include an endless belt heated by a heater and a pressing roller pressed against the endless belt to form a fixing nip therebetween through which a recording medium bearing a toner image is conveyed. As the recording medium is conveyed through the fixing nip, the endless belt and the pressing roller apply heat and pressure to the recording medium, melting and fixing the toner image on the recording medium.
Since the endless belt has a decreased heat capacity, it is heated by the heater quickly, shortening a warm-up time taken to heat the endless belt to a predetermined fixing temperature at which the toner image is fixed on the recording medium. For example, a metal heat conductor may be disposed opposite an inner circumferential surface of the endless belt. As the heater situated inside the substantially tubular, heat conductor heats the heat conductor, the heat conductor in turn heats the endless belt. A nip formation pad disposed opposite the inner circumferential surface of the endless belt presses the endless belt against the pressing roller to form the fixing nip between the endless belt and the pressing roller. A heat insulator is interposed between the heater and the nip formation pad to shield the nip formation pad from the heater. Thus, the heat insulator facilitates heating of the heat conductor and enhances durability of the nip formation pad.
However, the heat insulator, if it has an increased heat capacity, may decrease an amount of heat conducted to the heat conductor, degrading heating of the heat conductor. As a result, it may take longer to warm up the endless belt to the predetermined fixing temperature, consuming an increased amount of energy.